Vacuum diffusion pump



r0 mam 4 SYSTEM 30-; 3 .3, 5. I I I H 27 g 28 E'; 1 i SCREENS FOR FRACTIONATION Z9 l I6 f. I is 5 T /r0 FOREPUMP 24\ EJECTED cows/V5475 J lyizs, 1942. I R NELSON 2,291,054

v VACUUM DIFFUSION PUMF Filed Aug. I51,v 1959-- 70 VACUUM SYSTEM 2 "1153- z INVENTOR.

' R/CHARD B. NELSON ATTORNEY.

Patented July 28, 1942 UNITED STATES PATENT OFFICE VACUUM-DIFFUSION PUMP Richard B. Nelson, East Orange, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application August 91, 1939, Serial No. 292,911

8 Claims.

bons that are produced by decomposition during heating and condensing of oil used as a working liquid are trapped and removed from the pump. A further object of my invention is a pump which has ahigh pumping speed, will produce high ultimate vacuum, and will work against a comparatively high backing pressure, and also is mechanically rugged and commercially feasible for factory and laboratory applications. p

The invention is defined with particularity in the appended claims and preferred embodiments are described in the following specification and shown in the accompanying drawing in which Figure 1 shows a vertical sectional view of one pump embodying my invention and Figure 2 shows a vertical sectional view of another pump V embodying my invention.

Chamber I of my novel difiusion pump communicates through an inlet'port 2 at its upper end with the envelope to be evacuated and communicates throughoutlet port 3- with a preliminary or so-called rough pump. The rough pump is commonly referred to in the art as the fore pump or the backing pump. Pumping fluid 4, heated in the boiler in the bottom of the pump by an electric heater such as shown at 5, is vaporized and expelled in a downwardly directed jet from the annular nozzle 6. The nozzle 6 is formed by supporting sleeves I and 8 with their rims coaxial and flared to leave an annular opening. A downwardly directed jet of pumping fluid vapor is condensed on the cooled walls of the cylindrical condenser 9 centrally depending, ac-

- cording to Figure 1, from a disc I 0 sealed gastight into the upper end of the chamber. Condenser 9 comprises two concentric tubes with liquid cooling ports to the annular space between tube l2 above ring I3 should be of good heat insulating material so that tube I2 is cooled only at its lower end. The housing I4 comprising the inner wall of the condenser encloses the outlet end of cylinder l2 and communicates through port 3 to the fore pump. I

Gas molecules entering the chamber from the inlet port are entrained by the downwardly diercted vapor from jet 6 and impelled toward the next jet. The vapors condense upon the cooled condenser wall releasing the gas molecules which are then entrained toward the exhaust port by the next jet.

My novel pumping device is constructed to fractionally distill the fluid in-the bottom of the chamber and selectively .supply the different fractions to the different nozzles, so that only the most phlegmatic constituents are admitted to the nozzle nearest the vacuum end of the chamber, the more volatile constituents being directed to the nozzle nearest the outlet port. Conden-' sate from both nozzles drains down the inner surface of sleeve 1 to the junction with tube II, and hence to the center of the boiler through the liquid trap in pipe l5. Pipe 15 may drop the oil to the top of a stack of screens comprising, preferably, cones of wire mesh, piled with alternate cone inverted so that the oil trickles downward and wets all of the screens. Vapor rising from the boiler picks up and carries away the high volatiles on the screen much in themanner of the reflux still. cylinder areset in liquid-tight contact with the bottom plate of the chamber to divide the lowerend of the pump into concentric vapor generating compartments l8 and I1. Small openings I8 of such size are made in the lower end of tube 1 below the liquid level to permit slow flow of' liquid from chamber l6 into I! at the rate at which oil evaporates in chamber H. The most volatile constituents of the pumpingfluid drained into the inner compartment have sufflcient time to vaporize in the inner compartment and be conducted away to the nozzle I I before these constituents may flow into compartment l'l. Hence the constituents of lowest volatility are directed to nozzle 6. 1

To place in operation the desired pumping fluid is poured into the pump, the inlet port is connected to the envelope tobe evacuated, the outlet port connected to a. fore pump, cooling water is circulated in condenser 9 and the temperature of the bottom plate of the chamber raised to a point slightly above vaporization temperature of the most phlegmatic constituent of the pumping fluid. A jet of vapor of relatively high velocity is directed downwardly by nozzle 6 and upwardly by nozzle II, each nozzle receiving only the desired constituent of the pumping fluid. The first nozzle discharges the entrained Tubes 1 and 8 within the q pump. The vapor from nozzle I I, however, 'condenses on the wall of cylinder I2 and returns to the boiler, the heat given up by the vapor servingto keep the cylinder at a temperature above the condensing temperature of the contaminating volatiles, or "light ends of the pumping fluid which appear as a result of decomposition of the fluid. The much cooler walls of housing I4, however, condense these volatiles and drain them into the trap between the lower ends of cylinders I2 and 9 where they remain inactive. It has been found that oils used over and over in my improved pump never accumulate deleterious high vapor pressure constituents, such as volatiles and light ends, as the pump in operation continually purifies the oil.

The vacuum pump shown in Figure 2 embodies the characteristic featuresof my invention with some of the parts rearranged. The pump of Figure 2 shows my improved baflle at the input end of the pump directly above an improved high vacuum nozzle 20. Between nozzle 20 and the outlet nozzle II is added an intermediate nozzle 2|, each nozzle communicating through its individual conduit with the boiler of the pump. The conduits are concentrically arranged to form thr'ee concentric compartments 22, 23 and 24 at the lower end, the latter compartment being inside the other two and communicating with the high vacuum nozzle 20. Fractionation of the oil divides the oil into three groups of components and delivers them to their respective nozzles in the manner described, the condensate II, itswalls being held free of the walls of housing I4 so that the cylinder may be heated by the vapor from the nozzle. As in the pump of Figure 1 the temperature along cylinder I2 is highest at its outer end and coolest at the nozzle end. The temperature .gradient between the ends of the cylinder is automatically adjusted by the vapors flows inwardly toward the center of the pump. The high pumping speed of this nozzle is apparently due to the low number of ambulant vapor molecules flowing upwardly in the pump.

The baifie that cooperates with nozzle 20 to give best unidirectional flow to the gases comprises a plurality of concentric annuli 30, each annulus from each ofv thenozzles draining down the wall so that practically all of the vapors is condensed short of the outer-end of the cylinder and returned to the boiler. Baffle 26 may be placed across the outer end of the cylinder-to stop any vapor that may reach the .end of the cylinder. Gas, light end impurities and volatile contaminations, however, pass on into the housing where they are either pumpedaway by the. fore pump or are condensed by the cooler walls of thehon'sing and drained to the bottom of .the housing.- My improved pump is so efiective in separatingundesirable volatiles from the pumping fluid that kerosene or gasoline added to an oil pumping fluid commercially known as Apiezon oil is quickly isolated in housing I4. '1 1 The high vacuum nozzle 20 found to be most effective comprises a shallow 'd'upor hood 21 fitted over the rim of a sharp edged 28 with a small annular clearance between the' ring and the skirt of the hood. The diameter of the conduit 29 supporting the ring should be consider ably less' than the diameter of the hood so that comprising a ring, preferably tubular in shape and having an outwardly extending radial fl'n at the lower end of the ring, the fln of each ring underlying the end of the next larger ring. Each fin slopes outwardly and preferably downwardly to permit condensate to drain down into the pump. That portion of the baffle directly above nozzle 20 is closed with a solid shield ll. Gas flowing downwardly in a vertical direction passes between the vertical telescoped sections of the baflle and with one reflection from the radial fins of the baiile can pass to the cooled walls of chamber I, from whence it enters the stream of vapor from nozzle 20 and is carried downwardly toward the outlet port. Air or gas molecules are delivered directly by the baffle to the open annular space around the nozzle from which the molecules may pass unimpeded into the vapor stream. Any oil molecules, however, traveling upward from the nozzle 20'must, to reach the upper side of the baflle, be reflected twice from cool surfaces of the condenser and baflle. Bailles heretofore in common use. deliver the molecules to the space above the end of the high vacuum nozzle, so that the nozzle blocks off a large portion of the effective path through the battle. The top of my nozzle 20 may be placed close to the bailie without constricting the effective path. Further, elimination of. space between the nozzle andbaille of my pump reduces the number of reflections. below the baflle and minimizes the resistance to the gas flow.

A pumping speed of 280 liters of gas per second has been attained with a pump constructed as shown in Figure 2 with the following dimensions:

The inside. diameter of chamber I is 4% inches;

. inch; the inside diameter of cylinder I2 is 1 inch and its length is 5 inches; and the annular clearance between nozzle II and the cylinderis 181' inch. The clearance between the skirt of nozzle 21 and the wall of chamber I is A; inch.

Commercial pumping oil of the type known as Octoil when heated with a 500 watt electric heater pumped gas at the rate of 280 liters per second and obtained ultimate vacuum at 1x10 mm. of mercury measured with an ionization gauge calibrated with air. The chamber wall I of this pump is brass .065 inch in thickness and the"nozzle tubes and cylinder. I2 are steel .030 inch in thickness. The lower end of the chamber should insulated to reduce heat loss. The water through the jackets may be tap water at of the housing I! to facilitate removal of residues in the housing.

My improved. oil diffusion pump not only separates-thevarious constituents of the oil according to the volatility but removes contaminated oil and high vapor pressure residues from the pump.

thecenter of the stream of vapor from the'nozzle My pump has m h m speed; high perm"- sible backing pressure and is capable of high ultimate vacuums. A mechanically rugged pump may be fabricated from commercial metal tubing and may be handled roughly, and is commercially feasible for factory and laboratory uses.

I claim:

1. A vacuum pump comprising a tubular cylinder ported at one end, means to cool only said one end, a tubular nozzle co-axialwith said 1 cylinder and extending into said end of the cylinder with an annular space between the rim of the nozzle and the wall of the cylinder, a source of pumping vapor communicating with the nozzle, the inlet port of the pump communicating with said space, a housing enclosing the other end of said cylinder and joined gas tight to the cylinder along a line spaced from said other end, said other end of the cylinder being open and communicating with the interior of said housing, said other end of the cylinder being thermally insulated from surrounding structure oi the pump, and being thennally free to be heated by said vapor to a temperature near the condensing 5. A vacuum pump of the difiusion type adapted to employ a mixed organic working fluid com-' prising a cylinder, a nozzle at one end of the cylinder with an annular space between the rim of the nozzle and the wall of the cylinder, a source of vapor communicating with the nozzle, an inlet port oi. the pump communicating with the space, the other end of the cylinder communicating with the outlet port of the pump, and means for maintaining a diiierence in temperature between the ends of said cylinder, means for cooling said cylinder at its nozzle end to a temperature below the condensing temperature of said working fluid, the other end of the cylinder being thermally insulated and free to be heated by said working fluid to a temperature intermediate the condensing temperature of the working fluid and the temperature of volatile constituents in said fluid.

6. A vacuum pump of the diiiusion type adapted to employ an organic pumping fluid, said fluid containing gas, light ends and impurities more volatile than said fluid, an elongated cylinder,

temperatureor said vapor, and the outlet port of said pump communicating with said housing.

2. A vacuum pump of the diiiusion type adapted to employ a mixed organic working fluid comprising a nozzle for projecting a stream of vapor of the working fluid toward the outlet port of the pump, a cylinder open at each end coaxial with said nozzle to receive at one end the vapor stream from the nozzle, means for cooling said cylinder only at said one end, a housing spaced from and enclosing the cylinder, said housing being joined gas t ght to the cooled end of the cylinder and communicating with the outlet port of the pump, a boiler for evaporating th fluid, a conduit to conduct the evaporated working fluid to the nozzle, the other end of the cylinder being thermally insulated and free to be heated by said evaporated working fluid, a drain to return condensed fluid in the cylinder to the boiler.

3. A vacuum pump or the diffusion type comprising a tubular pumping chamber, a nozzle for directing an annular stream of the vapor of said fluid along the wall of said chamber toward one end 01' the chamber, a baflie in close spaced relation with said nozzle and between the nozzle and the other end ofthe chamber, said baiile comprising a plurality of coaxial annuli, each annulus having a tubular ring concentric with'the chamber, the ring being coaxially arranged in spaced telescoped relation, one within the other, and each ring having an outwardly extending radialflnatthenozzleend oithering,thefin oi. one annulus spaced from and overlying the end of the next larger ring.

4. Avacuumpump of the difl'usioniwpe com- 'prisingatubularpmnpchamberwithaninlet port and an outlet port, a nozzle with an annular opening concentric with the chamber for directing a stream of vapor toward the outlet port, a baflie across the chamber between the inlet port and the nomle comprising a plurality of annuli concentric with the chamber, each annulus having a tubular ring portion coaxial with the chamber and a radial fin portion extending toward the wall of the chamber, the tubular rings being arranged in spaced telescoped relation and the 1111 oi. each annulus overlying the nozzle end of the ring portion 01' the next larger annulus, the innermost annulus overlying the end 01' said nozale and the annular spaces between the flns opening directly to the pump chamber wall opposite said nozzle.

a nozzle at one end of said cylinder for projecting a stream of vapor of said fluid with its impurities toward the other end, a generator for vaporizing said fluid and means for conducting said vapor to said nozzle, means to maintain said one end oi. the cylinder at a temperature below the condensing temperature of said vapor and means for maintaining said other end at a temperature between the condensing temperature of said impurities and the condensing temperature or said vapor, means at said other end to remove and condense said gas and impurities, and means 7 to return the condensed vapor to said generator.

7. A vacuumpump comprising a tubular chamber with an inlet port and an outlet port, the ports being at opposite ends of the chamber, means to cool the chamber wall, a baflie across the chamber between the inlet port and outlet port comprising a plurality of coaxial annuli concentric with the chamber, each annulus having a tubular ring coaxial with the chamber, the rings being telescoped and concentric with and radially spaced from each other, and each ring having an annular iin at its end toward the outlet port, the fln of each ring overlying the end of the next larger ring, the fins being truncated cones coaxially arranged in spaced nested arrangement and sloped outwardly and'toward said outlet port so that the spaces between the has open obliquely to the pump chamber wall.

8. A vacuum pump of the diffusion type comprisingatubularpumpchamberwithaninlet port and an outlet port, means to cool the chamber'wall, a nozzle with an annular opening con. centric with the chamber for directing a stream of vapor toward the outlet port, means to deflect fluid to be pmnped, flowingaxially along the chamber from the inlet port, into the annular space between the nomle and the cooled chamber wall comprising a plurality of truncated cones coaxial with said chamber, said cones being grad- -uatedindiameterandbeinginspacednested relation with the smallest cone closely adjacent said nozzle and the successively larger cones arranged outwardly toward said cylinder wall, the sides of said cones being sloped outwardly and 'toward said outlet port, so that the space between the cones opens obliquely to the cooled pump chamber wall opposite said nozzle.

RICHARD B. NELSON. 

